Rolls the dice formula specified in the String diceRoll.
It generates the appropriate random dice rolls, makes the indicated
adjustments, then returns the result. It supports the following
notation:
+ - * / ( ) ndn nDn
Examples:
Roll("2d4") will return a value from 2 to 8.
Roll("3d6+3") will return a value from 6 to 18.
Roll("5*(1+2d8)/(3-1d2)") will return a value from 7.5 to
90.